Field of Application
The following description relates generally to telecommunications systems and wireless communications systems.
Prior Art
Channel estimation plays a key role in modern communications systems. When data is transmitted over a communications channel, the receiver needs the knowledge of the channel for data recovery, thus channel estimation is a critical function in the receiver. The quality of the channel estimation directly influences the receiver performance in terms of bit error rate and/or block error rate.
State-of-the-art wireless cellular networks employ highly spectrum-efficient transmissions such as high-order modulation and MIMO (multi-input multi-output). Such transmission schemes require even more accurate channel estimations in order to successfully recover data at the receiver. Typically channel estimation is derived from the correlation of a known pilot signal and the received signal. The accuracy of the correlation approach is limited by the correlation length and the signal-to-noise ratio (SNR), which can be poor when the channel changes rapidly or when the mobile user is at the cell edge. For example, in an OFDM (orthogonal frequency division multiplexing) network such as LTE (long-term evolution), the pilot signals are carried by certain subcarriers in frequency domain, and the channel at each pilot subcarrier can be estimated independently. If, however, the mobile user is at the edge of the serving cell, the interference from other neighbor cells can be much stronger than the pilot subcarriers. Consequently, the channel estimation quality can be very low.
The accuracy of the channel estimation can be improved by certain optimum approaches according to various criteria. Among them are least square (LS) and minimum mean-square error (MMSE). Those approaches, when applied to LTE systems, however, are often computationally intensive due to processing of large matrices, the dimension of which can be up to several hundreds. This is far beyond the processing power in the mobile-user devices to date and in the near future.
Accordingly, methods, apparatus, and systems that provide efficient and accurate channel estimation are highly desired.